1. Field of the Invention
The present invention relates generally to a process for making pyridazinone derivatives and a hydrazone aldehyde precursor.
2. Description of Related Art
Certain carboxy substituted 4-oxo-1,4-dihydropyridazines and carboalkoxy substituted 4-oxo-1,4-dihydropyridazines are known in the art to have plant gametocidal activity and plant growth regulatory activity. Current methods for producing the above compounds typically use expensive raw materials and/or result in low yields of product. For example, U.S. Pat. Nos. 4,707,181; 5,026,880; and 4,732,603 disclose preparing the above compounds by reacting a 2-phenylhydrazono-3-oxoglutarate with an organic acid chloride in the presence of a Grignard reagent (isopropyl magnesium chloride). The Grignard reagents are expensive and low yields are obtained. U.S. Pat. Nos. 5,189,163 and 5,010,192 also disclose using expensive raw materials, such as methyl-3-oxopentanoate, and result in low yields.
The present invention provides a more efficient process for making pyridazinone derivatives which results in higher yields of product and uses lower cost raw materials, hydrazone aldehyde and diazo acetate.
Hydrazone aldehydes are useful as precursors in the production of the carboxy substituted 4-oxo-1,4-dihydropyridazines and carboalkoxy substituted 4-oxo-1,4-dihydropyridazines mentioned above. Such hydrazone aldehydes, such as 4-chlorophenylhydrazone aldehyde (ethanedial, mono[(4-chlorophenyl)hydrazone]), have typically been made by batch processes, wherein one reactant is added to a reactor containing the other reactant. However, such batch processes lead to a lower payload (2-5%). An increase in the payload above 5% made the reaction slurry difficult to mix and thus resulted in by-product formation. In addition, the water content of the resulting solution is about 80% in a batch process, making the solution difficult to wash and handle, and causing filtration of the product to be very slow. The high water content also leads to very long drying times of the product.
An improved process to produce hydrazone aldehydes having a decreased water content would lead to a solution which is easier to handle, and decreased filtration and drying times of the product.